Wrong. If you will notice, I said "the earliest devices". They didn't use plutonium for nuclear devices until much later.
Much as I hate continuing to inject facts into an off-topic discussion... I wouldn't call it "much later". The first bomb *design* was the uranium gun-type bomb. They thought that they could use the same design with Pu239, but discovered when their first significant samples of Pu showed up that it just wouldn't work. The first bomb ever *detonated* (at Alamogordo, NM, on 16 July 1945) was an implosion bomb using plutonium. You see, the implosion design was sufficiently hairy that they needed to test it before using it for real. The "Los Alamos Primer" I cited yesterday contains a photo captioned: "Sgt. Herbert Lehr delivering plutonium core of first test bomb in its shock mounted case to the assembly room at McDonald Ranch, on the Trinity test site in the desert northwest of Alamogordo, NM, July 12 1945." (The "shock mounted case" in question is a rectangular box, roughly 6"x6"x8") - Bill